The present invention relates to the formation of dielectric layers during fabrication of integrated circuits on semiconductor wafers. More particularly, the present invention relates to a method for providing a dielectric film having a low dielectric constant that is particularly useful as a premetal or intermetal dielectric layer.
One of the primary steps in the fabrication of modem semiconductor devices is the formation of a thin film on a semiconductor substrate by chemical reaction of gases. Such a deposition process is referred to as chemical vapor deposition or xe2x80x9cCVD.xe2x80x9d Conventional thermal CVD processes supply reactive gases to the substrate surface where heat-induced chemical reactions take place to produce a desired film. Plasma enhanced CVD techniques, on the other hand, promote excitation and/or dissociation of the reactant gases by the application of radio frequency (RF) or microwave energy. The high reactivity of the released species reduces the energy required for a chemical reaction to take place, and thus lowers the required temperature for such PECVD processes.
Semiconductor device geometries have dramatically decreased in size since such devices were first introduced several decades ago. Today""s fabrication plants are routinely producing devices having 0.25 xcexcm and even 0.18 xcexcm feature sizes, and tomorrow""s plants soon will be producing devices having even smaller geometries. In order to further reduce the size of devices on integrated circuits, it has become necessary to use conductive materials having low resistivity and insulators having a low dielectric constant. Low dielectric constant films are particularly desirable for premetal dielectric (PMD) layers and intermetal dielectric (IMD) layers to reduce the RC time delay of the interconnect metalization, to prevent cross-talk between the different levels of metalization, and to reduce device power consumption. Undoped silicon oxide films deposited using conventional CVD techniques may have a dielectric constant (k) as low as about 4.0 or 4.2. One approach to obtaining a lower dielectric constant is to incorporate fluorine in the silicon oxide film. Fluorine-doped silicon oxide films (also referred to as fluorine silicate glass orxe2x80x94xe2x80x9cFSGxe2x80x9d films) may have a dielectric constant as low as about 3.4 or 3.6. Despite this improvement, films having even lower dielectric constants are highly desirable for the manufacture of integrated circuits using geometries of 0.18 xcexcm and smaller. Numerous films have been developed in attempts to meet these needs including: a spin-on glass called HSQ (hydrogen silsesqui-oxane, HSiO1.5) and various carbon-based dielectric layers, such as parylene and amorphous fluorinated carbon. Other low-k films have been deposited by CVD using an organosilane precursor and oxygen to form a silicon-oxygen-carbon (Sixe2x80x94Oxe2x80x94C) layer.
While the above types of dielectric films are useful for some applications, manufacturers are always seeking new and improved methods of depositing low-k materials for use as IMD and other types of dielectric layers. For example, in some applications, it is desirable to heat the walls of the chamber in which deposition takes place in order to optimize the deposition reaction. Unfortunately this can cause the organosilane to react undesirably before reaching the chamber, thereby reducing the deposition rate.
The disadvantages associated with the prior art are overcome by an apparatus and method for depositing thin films. The apparatus generally comprises a process chamber having one or more walls and a lid and two heat exchangers. A first heat exchanger is coupled to the walls and a second heat exchanger is coupled to the lid. The two heat exchangers are configured to provide separate temperature control of the walls and lid of the chamber. In one embodiment, the first heat exchanger is coupled to a first plurality of passages in the walls and the second heat exchanger is coupled to a second plurality of passages in the lid. Heat transfer is effected by fluids circulating with the passages. The apparatus may further comprise a gas delivery system having a gas distribution manifold attached to the lid and a substrate holder with a heater. Such a configuration is desirable in an apparatus for depositing thin films with organosilanes. Separate control of the lid and wall temperatures inhibits reaction of the organosilane within the gas distribution manifold while optimizing reaction of the organosilane within the chamber.
The method of the present invention deposits a carbon-doped silicon oxide layer using a thermal, as opposed to plasma, CVD process. The substrate can be heated during densification. The method is particularly suitable for deposition of low dielectric constant films using methylsilane or di-, tri-, tetra-, or phenylmethylsilane and ozone. In one embodiment, the layer is deposited from a process gas of ozone and an organosilane precursor having at least one silicon-carbon (Sixe2x80x94C) bond. During the deposition process, the substrate is heated to a temperature less than about 250xc2x0 C. In some embodiments, the organosilane precursor has a formula of Si(CH3)xH4xe2x88x92x where x is either 3 or 4 making the organosilane precursor either trimethylsilane (TMS) or tetramethylsilane (T4MS). In one specific embodiment, the process gas is a mixture of TMS, ozone and helium to deposit a low k carbon-doped silicon oxide film. In other embodiments, the substrate over which the carbon-doped oxide layer is deposited is heated to a temperature of between about 100-200xc2x0 C. and the deposition is carried out in a vacuum chamber at a pressure of between 1-760 Torr. In still other embodiments, the carbon-doped silicon oxide layer is cured after it is deposited to minimize subsequent moisture absorption. Curing can be done in either a vacuum or conventional furnace environment.
The above-described apparatus can be incorporated into a substrate processing system directed by a controller operating under the direction of a computer program. The system and apparatus can implement the method for forming a layer of material over a substrate.
The apparatus, method, and processing system are particularly useful in the manufacture of sub-0.2 micron circuits as it can form a PMD or IMD film with a dielectric constant below 3.0. The film has good gap fill capabilities, high film stability and etches uniformly and controllably when subject to a chemical mechanical polishing (CMP) step.
These and other embodiments of the present invention, as well as its advantages and features, are described in more detail in conjunction with the text below and attached figures.